This invention relates generally to hyperspectral imagers or imaging spectrometers, and, more particularly, to more compact hyperspectral imager designs.
A hyperspectral imager is a conventional device that is commonly used to examine the spectral, or wavelength dependent, content of light. Light emitted or reflected by a given object or scene is imaged by some means onto an aperture, usually a slit element that transmits a single line image from the object or scene. A spectrometer then re-images this light to another location while dispersing this light according to its wavelength in a direction orthogonal to the orientation of the slit element, where it can readily be observed or recorded.
Because every material has a unique spectral signature, the spectrometer has become a very useful scientific tool in a broad range of scientific and industrial applications including, but not limited to, the monitoring of regional and global environmental conditions, the identification of both airborne and terrestrial objects and threats in surveillance imagery for military applications, the assessment of unknown substances in forensic applications, the precise characterization of color spectra in colorimetry, and in the assessment of crop health and irrigation scheduling in the farming industry.
Current physically compact spectrometer design forms, like the Offner and Dyson configurations, require curved dispersing elements. These can be very difficult and costly to build, particularly in the long-wave infrared wavelengths (7.5 to 14 micrometers).
Current hyperspectral imager designs are either too large in size for many applications, including but not limited to, unmanned aircraft surveillance and forensic fieldwork, or their dispersing elements are too complex and costly to fabricate for commercial applications, or they do not provide enough spatial and spectral imaging quality to meet the required system performance, or they cannot provide a combination of these characteristics simultaneously. For example, consider some applications of hyperspectral imaging in which it is desirable, and not available in current designs, to have an optical system that simultaneously possesses a large spectral bandwidth such as the combined visible, near infrared and shortwave infrared bands, a large spatial field so that a large ground area can be covered with a single fly-over, high spatial and spectral resolutions so that small spatial and spectral features can be resolved, negligible spectral and spatial distortions to facilitate recognition algorithms, a very small size and mass so that the system can be transported in an unmanned aerial vehicles (UAV) or be man-portable, and is readily manufacturable from low-cost components.
There is therefore a need for a spectrometer design that is more compact in physical size than current spectrometers.
Furthermore, there is also a need for a spectrometer design that is lower in mass than current spectrometers.
Furthermore, there is also a need for a spectrometer design that utilizes less complex and costly dispersing elements.
Furthermore, there is also a need for a spectrometer design that provides a high degree of spatial and spectral image quality that is relatively free of spatial and spectral image distortions.
Furthermore, there is also a need for a spectrometer design that provides larger spatial and spectral fields than current spectrometers.
Still further, there is also a need for a spectrometer design that provides a combination of the characteristics described above with superior trade-offs than have been previously attainable.